1. Field of the Invention
The present invention relates to a multiplex transmission method used in, e.g., a vehicle and, more particularly, to a multiplex transmission method for, when a transmitted new signal frame is not normally received, re-transmitting the new signal frame.
2. Description of the Related Art
In recent vehicles, the number of electronic devices equipped in a vehicle is considerably increased along with the development of electronic control, and this results in an increase in the number of wiring lines for connecting the electronic devices, and a complicated wiring structure. In order to solve these problems, as disclosed in, e.g., Japanese Laid-Open Patent Application No. 61-224534, a multiplex transmission method has been examined, and is beginning to be put into practical applications. In this method, signal transmission operations among a plurality of electronic devices are performed in a multiplex transmission mode, i.e., communication nodes of the plurality of electronic devices are connected to a common transmission path, and signal transmission operations among the communication nodes are performed in the multiplex transmission mode.
In the above-mentioned multiplex transmission method, when each communication node transmits a signal frame for informing its own information, it checks if the signal frame is normally received. If the communication node determines that any of nodes to receive the signal frame did not normally receive the signal frame, it re-transmits the signal frame.
When the signal frame is re-transmitted, as described above, if information in the signal frame is merely information for controlling an ON/OFF state of a switch, no problem is particularly posed. However, if the information is percent control information for, e.g., decreasing an engine output by 50%, a reception node must check if the signal frame is a new frame, which has not been received by the self node yet, or is a re-transmitted one of the already received frame.
When the information in the signal frame instructs to decrease an engine output by 50%, one of a plurality of nodes, which must receive the signal frame, is an EGI node having an EGI controller for controlling an engine, and the signal frame is normally received by the EGI node but is not normally received by another node, the following drawback occurs. More specifically, if the EGI node cannot detect that the re-transmitted signal frame is a re-transmitted one of the already received frame, it receives the re-transmitted frame as a new frame, which is not received yet, and decreases an engine output by another 50%. As a result, the engine output is decreased to 25%.